Elongated heat-generating apparatus providing for a reduction in the highest voltage to be applied

ABSTRACT

An elongated heat-generating apparatus is divided into at least two sections and a transformer is provided at each division between adjacent sections of said at least two sections and linked with the electrical circuits of the adjacent sections. The output voltage of the transformer is as near as possible to the highest voltage allowed for the section, the resistance of which is adjusted in relation to the definite voltage to meet the required quantity of heat in that section.

limited States Patent [1 1 Ando 1 Aug. 28, 1973 [54] ELONGATEDHEAT-GENERATING 3,293,407 12/1966 Ando 219/301 APPARATUS PROVIDING FOR A3,575,581 4/1971 Ando 219/301 REDUCTION IN THE HIGHEST VOLTAGE TO BEAPPLIED Masao Ando, Kahokuku, Kanagawa, Japan Inventor:

Chisso Corporation, Osaka, Japan Nov. 16, 1971 11.8. CI 219/301,219/1049, 219/300, 219/477, 307/83, 323/44 R, 338/295 int. C1. H051)3/00 Field of Search 219/300, 301, 10.49, 219/1051, 535, 477;-307/54,69, 83; 323/44 R; 338/295 References Cited UNITED STATES PATENTS 8/1970Ando 219/300 8/1971 Ando 219/300 Primary Examiner-A. BartisAttorney-Fred C. Philpitt 5 Claims, 7 Drawing Figures PATENTEflmza msFIG. l

PRIOR ART FIG. 7

FIG; 5 FIG. 6

ELONGATED HEAT-GENERATING APPARATUS PROVIDING FOR A REDUCTION IN THEHIGHEST VOLTAGE TO BE APPLIED BACKGROUND OF THE INVENTION The presentinvention relates to an elongated electrically heat-generating apparatusto be used as a heat source for, e.g. a pipeline which requires heatingor temperature-maintenance such as a long-distance pipeline fortransporting heavy fuel oil, in which apparatus the highest voltage ofits circuit is limited to as a value as possible, and the electric powernecessary therefor is provided from one electric source.

Although the present invention can be applied to any heat-generatingapparatus in which an elongated, electrically resistant body is used asa heat-generating body, it will be herein illustrated in reference to aheatgenerating apparatus utilizing skin effect current which isapplicable particularly advantageously in the present invention.

The heat-generating apparatus utilizing skin effect current referred toherein comprises a ferromagnetic pipe and an insulated electric wirepassing through the inside of the pipe, one end of said insulated wirebeing connected to one end of said ferromagnetic pipe remote from ana.c. source, the other ends of said insulated wire and saidferromagnetic pipe being both connected to the a.c. source, and the wallthickness of said ferromagnetic pipe being greater than twice the depthof skin of the a.c. flowing therethrough. Such a heatgeneratingapparatus utilizing skin effect current is described in my US. Pat. No.3,293,407 which is assigned to the assignee of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention along with itsbackground will be illustrated referring to the accompanying drawingsfor the better understanding.

FIG. ll shows a cross-sectional view of a known heatgenerating pipeutilizing skin effect current to which the present invention can beapplied; FIG. 2, a schematic view of circuit for illustrating theprinciple of the heat-generating apparatus of the present invention;FIG. .3, a schematic view of the voltage distribution of theheat-generating apparatus of the present invention; FIG. 4, across-sectional schematic view of a pipeline to which theheat-generating apparatus of the present invention is applied forheating it; and FIGS. 5, '6 and 7, cross-sectional views ofheat-generating pipes utilizing skin effect current to which the presentinvention is applied.

DETAILED DESCRIPTION OF THE PRIOR ART In FIG. I, which illustrates theprior art pipe heating systems, a ferromagnetic pipe 1, e.g. a steelpipe, is shown and 2 shows an insulated electric wire passing throughthe inside of said ferromagnetic pipe, one end of said wire beingconnected to one terminal of an a.c. source 3, and the other end thereofbeing connected to one end 6 of said ferromagnetic pipe remote from thea.c. source. The other end 5 of said ferromagnetic pipe I near to thea.c. source is connected to the other terminal of the a.c. source 3 bymeans of an electric wire 4. Thus, alternating currents 7 and 7 flow.Numeral 9 shows a power transmission line to the a.c. source 3.

Further, if necessary, a short-circuit electric wire 8 for shorting theinside of the pipe can be used, through which an alternating current 7"flows. The effectiveness of such a short-circuit electric wire 8 isdescribed in my detail in US. Pat. No. 3575581, also assigned to theassignee of this application.

The point of the effectiveness of the short-circuit electric wire 8 inthe present invention is that the quantity of heat to be generated inthe whole of the heatgenerating apparatus utilizing skin effect current,can be thereby adjusted.

Now, in the circuit of FIG. 1, if the resistivity of the ferromagneticpipe is p(Q cm), the specific permeabilit y is u, and the frequency ofthe power source is f (Hz), the so-called depth of skin, S (cm)is cit--pressed as follows: I

$55030 P/ (if) With this S, if the wall thickness of the abovementionedferromagnetic pipe 1 is t( cm), the length is l(cm), and the innerdiameter is d (cm), and further if there is the following relationshipbetween them,

then the current 7' flowing through the ferromagnetic pipe 1 flowsconcentratedly only through the inner skin portion of the ferromagneticpipe 1, and substantially no voltage appears on the outer surface of theferromagnetic pipe. Accordingly, even if the outer surface of theferromagnetic pipe is shorted by a low impedance conductor,substantially no current flows therethrough, and also even if aconductive substance to be heated is contacted with the outer surface,substantially no flow of current to the substance is observed. Due tosuch safety, the ferromagnetic pipe can be utilized as a heat-generatingpipe.

In such a heat-generating apparatus, the heat generated along the innerskin portion of the heat-generating pipe amounts to 80 90 percent of thetotal heat, and the remainder is generated in the insulated electricwire 2. Accordingly, if both the ends 5 and 6 of the heatgenerating pipe1 are short-circuitted by a short-circuit electric wire 8, passingthrough the inside of the pipe as seen in FIG. 1, then a part of thecurrent 7 (shown in 7") flows through the short-circuit electric wire toreduce the apparent resistance of the heat-generating pipe. Thus, ifthe'current 7 is maintained at the same value, the heat to be generatedis reduced. The voltage necessary for such a heat-generating pipeutilizing skin effect current, is 300 700 V if an alternating current of50 60 Hz is used for the electric source, a steel pipe having an innerdiameter of l 3 cm is used as the ferromagnetic pipe, and an a.c. of I00200A is passed through the insulated electric wire. Thus, if the lengthof the heat-generating apparatus as shown in FIG. 1 is 40 km, at least12 KV is necessary for the voltage of the electric source 3. However, itis practically very difficult to use an insulated electric wire to whicha voltage of 12 RV is applied, in the inside of such a heat- SUMMARY OFTHE INVENTION The object of the present invention is to provide anapparatus in which a much lower voltage than 12 KV is utilized, for theinsulated electric wire, in the abovementioned case.

The present invention resides in an elongated heatgenerating apparatuswhich comprises an elongated electrically heat-generating body, andconductors connecting both the terminals of said body to an electricsource, said body and said conductors being both divided into at leasttwo sections and a transformer being inserted at each divided pointthereof, the input side of said transformer being connected to a sectionnear to said source, while the output side being connected to anadjacent section remote from said source, the output voltage of saidtransformer being as near as possible to the highest voltage allowed forthe section on the output side, the capacity of said transformercorresponding to the loads obtained by substracting, from the total loadof all the sections, the sum of the loads of all the preceding sectionsnearer to said source, and the resistance of each section correspondingto the quantity of heat required to generate in each section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, the presentinvention will be illustrated referring to FIG. 2 and followingdrawings.

In FIG. 2, a heat-generating pipe (a ferromagnetic pipe) and aninsulated electric wire as seen in FIG. 1, are both divided into foursections, 10 l4; l1 I5; 12- 16; and 13 17. It is now assumed for easyunderstanding that the length of the heat-generating pipe is dividedinto four equal sections and the resistance of the heat-generating pipein each section is uniform in the longitudinal direction of the pipealthough such equal length and such uniformity of resistance are notalways necessary, and in some cases, unequal length and non-uniformityof resistance would be preferable.

The heat-generating body in FIG. 2 can be considered to correspond tothe heat-generating pipe 1 in FIG. 1; the electric wire 14, to theelectric wire 2; the transformer 18, to the electric source 3; and thecurrent 22, to the current 7. It is assumed that the value of thecurrent 22 is i; the output voltage of the transformer 18 is V and alsothis V'is the highest allowable value; and in this case, theshort-circuit electric wireof FIG. 1 is omitted. In such an apparatus,the potential difference between the insulated electric wire 14 and theheat-generating'pipe, as shown by the straight line 30 in FIG. 3, is Von the output side of the transformer 18, while it is zero at the pointremotest from the transformer 18, that is, at the right end of theheatgenerating pipe 10. In this case, since the circuit current is i,the output capacity of the transformer 18 is Vi.

Next, the circuit of the section on the input side of the transformer 18will be illustrated. In this circuit, too, the voltage on the outputside, of the transformer 19 is assumed to be the highest one V allowedfor the insulated electric wire 15. In order to make the quantity ofheat to be generated in the heat-generating pipe 11 equal to that at theheat-generating pipe 10, the current 23 must be 2 1, since the lengthsof the heatgenerating pipes 10 and 11 are equal as mentioned above, andthe voltage on the input side, of the transformer 18 must be V/2. Thus,the output capacity of the transformer 19 is 2 Vi which is twice thecapacity of the transformer 18. If this consideration is further appliedto the circuits relative to the sections on the input side of thetransformers l9 and 20, the voltages and currents on the input andoutput sides, of the transformers 18, 19, and 21, and the outputcapacities I thereof are as shown in the following table. Thedifferences between the output capacities of the adjacent transformersare all vi.

In this table, the voltage and current on the input side, of thetransformer 21 and not shown since they are dependent on the voltage ofthe transmission line 26 and this has nothing to do with the presentinvention.

The potential difference between the insulated electric wire 15 and theheat-generating pipe 11 is shown by the straight line 29 in FIG. 3; thepotential difference between the insulated electric wire 16 and theheat-generating pipe 12, by the straight line 28; and the potentialdifference between the insulated electric wire 17 and theheat-generating pipe 13, by the straight line 27. As seen from thetable, the current 24 must be 3i and the current 25 must be 4i.

The dotted line in FIG. 3 shows the potential difference distributionbetween the insulated electric wire and the heat-generating pipe in casewhere the abovementioned division is not carried out. As apparent fromthis figure, if the division is not carried out, the voltage of thesource is 4 V which is four times that in the case of the division intofour sections.

Now, in order to equalize heat-generation per unit length of each foursection when the respective voltages and currents on the output side aregiven as above, there must exist the following relationships among eachresistance per unit length, of the heat-generating circuit in eachsection:

wherein R is the resistance per unit length, of the heat-generatingcircuit in the section on the output side of the transformer 18; R isthat in the section between the transformers 19 and 18;R, is that in thesection between the transforrners 20 and 19; and R is that in thesection between the transformers 21 and 20.

As for the method for holding such relationships in the heat-generatingapparatus utilizing skin efiect current, adjustment of R R and R (if Ris fixed in the above-mentioned formula (3)) by means of a shortcircuitelectric wire as shown as numeral 8 in FIG. 1, or the like, and/oradjustment by varying the diameter or material of the ferromagneticpipe, can be exemplified.

Various modifications corresponding to the shortcircuit electric wire 8are illustrated in FIGS. 5, 6 and 7.

According to the method of FIG. 5, an electric wire 35 coated by aninsulating layer 36, corresponding to the electric wire 2 in FIG. I, ispassed through the inside of a ferromagnetic pipe 37 as mentioned above,and further, a short-circuit electric wire 38 corresponding to theshort-circuit wire 8 in FIG. 1 is passed through the clearance part 39inside the ferromagnetic pipe 37. In this case, the short-circuitelectric wire 38 is not necessary to be insulated.

In FIG. 6, an electric wire 40 coated by an insulating layer 41,corresponding to the electric wire 2 in FIG. 1, is passed through theinside of a ferromagnetic pipe 43, but the insulated electric wire hasfurther on its surface, a metallic tape shield 42 for preventing coronadischarge which corresponds to the short-circuit electric wire 8 inFIG. 1. If the metallic tape is insufficient for adjusting theresistance, a means corresponding to the short-circuit electric wire 38in FIG. 5 can be added.

In FIG. 7, an electric wire 44 coated by an insulating layer 45,corresponding to the electric wire 2 in FIG. 1 is passed through theinside of a ferromagnetic pipe 46, and further an electricallyconductive metal 47 such as metallic sodium, is melt-filled (that is,filled through melting the metal) in the clearance part inside theferromagnetic pipe, which metal has properties of melting at arelatively low temperature and not corroding the insulating layer 45when it is filled in the clearance part, (in other words, melting atsuch an extent of temperature that the insulation of the insulatedelectric wire is not broken at the temperature), and corresponds to theshort-circuit electric wire 8 in FIG/1.

In FIG. 4 showing a laterally cross-sectional view of a pipeline towhich a heat-generating apparatus as mentioned above is applied forheating it or maintaining the temperature, numeral 31 shows atransporting main pipe; numeral 33, a ferromagnetic pipe correspondingto the pipe 1 in FIG. 1; numeral 32, an insulated wire corresponding tothe wire 2 in FIG. 1; and numeral 34, an insulating layer. Theexplanation as to the mutual relationship among the elementsconstituting the heatgenerating apparatus of FIG. 4 will be unnecessary.

The present invention relative to an elongated heatgenerating apparatuslimiting the highest voltage as described above referring to theheat-generating apparatus utilizing skin effect current, can be alsoapplied to an elongated electrically heat-generating body e.g. aninorganic-insulated metal sheath cable (referred to usually as Mlcable), other than the heat-generating apparatus utilizing skin efi'ectcurrent, but the case applied to the heat-generating apparatus utilizingskin effect current is most economical.

The above-mentioned equal division is not always necessary, but, in mostcases, it is most economical.

The present invention has an advantage in that the voltage applied tothe insulated electric wire is much reduced by the division as seen inFIG. 3, but has disadvantages in that transformers are required at eachdivided point; an insulated electric wire having a large capacity ofcurrent must be used in the heat-generating pipes excluding the finalsection; and means are needed to satisfy the above-mentioned formula (3)in order to prevent the increase of heat generation per unit length ofeach section except the final one, accompanied by the increase in thecurrent. However, in the provision of transformers at each divided pointwhich is most problematical among the above-mentioned countermeasures,single-layer winding transformers can be used as apparent from FIG. 2,and hence the provision is not so much an economical burden. In the caseof the above-mentioned heat-generating apparatus laid over a distance of40 km, the present apparatus was more economical as compared with thecase where a transmission line is provided along a long pipeline andfeeding transformers are provided at each divided point.

In the above-mentioned consideration, the power factor of the circuit inthe heat-generating pipe is assumed to be I, but the above-mentionedconsideration is not changed even when the power factor is a littleworse.

What is claimed is:

1. Elongate electrical heat generating apparatus comprising:

an elongate electrically conductive heat generating body which isdivided into at least two sections,

a transformer for each of said sections,

a source of alternating electric power,

circuit means including the secondary of each said transformer and alsothe associated section of said conductive body for passing an electriccurrent along the length of said section,

said circuit means further including the primary of the transformer forthe next said section more remote from said source for energizing saidprimary with the current passing through the associated section,

each said transformer providing across its secondary windingsubstantially the same predetermined voltage,

said transformer secondaries further providing different respectivecurrent amplitudes with each such secondary for a section of saidconductive body nearer said source providing a current amplitude greaterthan that provided for the next more re mote section,

and means for providing different electrical resistances for therespective said circuit means associated with said transformersecondaries to provide a predetermined heat output per unit length foreach said section.

2. The heat generating apparatus of claim 1 wherein each said section ofsaid conductive body comprises a section of ferromagnetic pipe,

said circuit means including an insulated electric wire passing throughthe inside of the respective associated pipe section,

the end of said wire nearer said source being connected through thesecondary of the transformer associated with the respective section tothe end of the pipe nearer said source and the other end of said wirebeing connected through the primary of the transformer associated withthe next more remote section to the other end of said pipe,

the wall thickness of said pipe being greater than twice the skin depthof the alternating current.

3. A heat-generating apparatus according to claim 2, wherein theferromagnetic pipe, in at least one section other than the sectionremotest from said a.c. source, is short circuited by a conductorpassing through the inside of said ferromagnetic pipe and connected tothe opposite ends of said pipe to provide thereby said means providingdifferent electrical resistance for said sections.

4. A- heat-generating apparatus according to claim 3, wherein theinsulated wire passing through the inside of the ferromagnetic pipe inat least one section has a me- 8 said ferromagnetic pipe, said metalhaving a melting temperature at which the insulation of the insulatedelectric wire passing through the inside of the ferromagnetic pipe isnot damaged.

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1. Elongate electrical heat generating apparatus comprising: an elongateelectrically conductive heat generating body which is divided into atleast two sections, a transformer for each of said sections, a source ofalternating electric power, circuit means including the secondary ofeach said transformer and also the associated section of said conductivebody for passing an electric current along the length of said section,said circuit means further including the primary of the transformer forthe next said section more remote from said source for energizing saidprimary with the current passing through the associated section, eachsaid transformer providing across its secondary winding substantiallythe same predetermined voltage, said transformer secondaries furtherproviding different respective current amplitudes with each suchsecondary for a section of said conductive body nearer said sourceproviding a current amplitude greater than that provided for the nextmore remote section, and means for providing different electricalresistances for the respective said circuit means associated with saidtransformer secondaries to provide a predetermined heat output per unitlength for each said section.
 2. The heat generating apparatus of claim1 wherein each said section of said conDuctive body comprises a sectionof ferromagnetic pipe, said circuit means including an insulatedelectric wire passing through the inside of the respective associatedpipe section, the end of said wire nearer said source being connectedthrough the secondary of the transformer associated with the respectivesection to the end of the pipe nearer said source and the other end ofsaid wire being connected through the primary of the transformerassociated with the next more remote section to the other end of saidpipe, the wall thickness of said pipe being greater than twice the skindepth of the alternating current.
 3. A heat-generating apparatusaccording to claim 2, wherein the ferromagnetic pipe, in at least onesection other than the section remotest from said a.c. source, is shortcircuited by a conductor passing through the inside of saidferromagnetic pipe and connected to the opposite ends of said pipe toprovide thereby said means providing different electrical resistance forsaid sections.
 4. A heat-generating apparatus according to claim 3,wherein the insulated wire passing through the inside of theferromagnetic pipe in at least one section has a metallic tape shieldthereon and the metallic tape shield is utilized as the short circuitingconductor.
 5. A heat-generating apparatus according to claim 3, whereinthe short circuiting conductor comprises an electrically conductivemetal which is melt-filled inside said ferromagnetic pipe, said metalhaving a melting temperature at which the insulation of the insulatedelectric wire passing through the inside of the ferromagnetic pipe isnot damaged.